With $3 million already spent to finish second in June’s primary, Democrat Ro Khanna will have to find a better way to use what little money he has left if he is to have any hope of unseating incumbent Rep. Mike Honda, experts say.

Khanna, a former Obama administration official from Fremont, has spent more than twice as much so far as Honda, D-San Jose, and about 3½ times as much per vote in the primary, making the 17th Congressional District one of the nation’s most expensive House races.

In the June 3 primary, Honda earned 48 percent of the vote and Khanna had 28 percent.

Now, as the race shifts gears toward November’s general election in the heart of Silicon Valley and the nation’s first mainland Asian-American majority district, Khanna has less money than Honda to run down the home stretch. And given Honda’s recent rate of fundraising, it’s unlikely Khanna can close the money gap.

“Khanna still has a remarkable amount of work to do if he wants to win this race,” said Kyle Kondik, a congressional elections expert at the University of Virginia’s Center for Politics. “Has he gotten a ton of traction? I would say no.”

A San Jose State University political expert who’s watching the race closely said the primary has been a tough, costly lesson for Khanna.

“With the money that Honda now has and the 20-point differential, the Khanna people are going to have to do some pretty extraordinary work to make it happen,” said political science professor Larry Gerston. “I guarantee you these people are spending a lot of time looking at things precinct by precinct, ethnic group by ethnic group, political party by political party to see where they can be more successful come November.”

Khanna’s campaign contends it achieved what it had to in the primary, boosting a previously unknown candidate who started out about 3 percent in early polls into the top two — defeating a pair of Republicans to trigger a Democrat-vs.-Democrat showdown in November.

“We’re really happy with the investments we made,” spokesman Tyler Law said, likening the campaign to a Silicon Valley startup — higher costs to build the initial infrastructure, followed by a more modest operating budget.

The staff and organization Khanna built over the past year remain solid for the general election, he said. “We can build on that … and we know we’re going to have the resources we need to make that closing argument to voters.”

A breakdown of Khanna’s spending in this year’s first half shows the largest chunk of money — about $767,000 — went to broadcast advertising. Next costliest was direct mail, about $365,000; $250,000 for staff salaries; $66,000 for printing and communication services or consulting; $65,000 for campaign strategists; and $53,000 in other media consulting and production costs.

Honda’s less lavish spending in the same six months included $209,000 for salaries, $179,000 for direct mail, and $111,000 to consultants and research firms. That latter figure included $29,000 for VR Research, a firm that gathers “opposition research” on clients’ rivals.

By the end of June, Honda’s campaign had about $1.06 million in the bank. Khanna, after accounting for some debts yet to be paid, had about $629,000.

Khanna’s campaign prides itself on applying the same microtargeting and precinct-level organization that carried President Barack Obama to victory in 2008 and 2012. His chief campaign consultant is Jeremy Bird, formerly national field director for Obama’s re-election campaign. Khanna’s team also includes Larry Grisolano, Obama’s ad-buying chief, and that’s where the real money went. Khanna aired four television ads from March through the primary; Honda has yet to air any.

“The fact that Khanna was on TV so much … shows that is still the tool for these races,” Kondik said. “But he was up on the air unanswered, and it didn’t really have much of an effect, it seems.”

Law insisted that Honda looks vulnerable, with a majority of primary voters having “said they want someone other than Mike Honda representing them.” But Kondik said the rule of thumb in most of the country, where House races still have traditional, partisan primaries, is to see how the incumbent did among his or her party’s own voters — if it’s less than 60 percent, the incumbent is in trouble.

In this race, Honda got 63 percent of the Democratic votes, Kondik said. He noted that when then-Rep. Pete Stark in 2010 won only 53 percent of Democratic votes, challenger Eric Swalwell went on to win the general election.

The $120 per vote that Khanna spent might seem like a lot, Gerston said, but given his low name recognition compared to seven-term incumbent Honda, “an almost 4-to-1 ratio is not that unusual.”

“Khanna is just trying to race uphill, and he put together a phenomenal staff,” Gerston said. “You can see that a lot of money went to that.”